This invention relates to a process for the production of flame resistant CFC-free (i.e., chlorofluorocarbon-free) rigid polyurethane foams.
The replacement of chlorofluorocarbon (hereinafter "CFC") blowing agents in rigid polyurethane foams with other blowing agents such as CO.sub.2, is problematical because the density of the foam has to be increased to obtain dimensional stability and the burning behavior of the foam is generally impaired.
The use of hydrocarbons, for example pentane, as blowing agents enables foams having "normal" densities of around 30 kg/m.sup.3 to be produced. However, these hydrocarbons have a significant adverse effect on the burning behavior of the foam. In order to improve the flame resistance of rigid foams of this type, inclusion of various solid flameproofing agents in the foam forming mixture has been proposed. See, for example GB-A 2,177,405, GB-A 2,177,406 or EP-A 239 891. However, these solid flameproofing agents have significant disadvantages. They are difficult to dose in continuous production processes carried out under high pressure. They also cause embrittlement of the rigid foams.